HATEFEST: Jubilant opponents of Margaret Thatcher gather yesterday in London, carrying a banner oozing venom. British social-media sites also exploded with loathing for the former PM. Photo: AFP/Getty Images

With “the mouth of Marilyn Monroe and the eyes of Caligula,” as French President François Mitterand described her, Margaret Thatcher transformed a reluctant Britain like no other peacetime leader before or since.

At the time Thatcher rose to power in the 1970s, the triumph of the left could be measured in the mountains of uncollected rubbish on the streets, the picket lines that forced some hospitals to close to all but emergency cases, and the bodies that gathered in the morgue.

Striking labor unions seeking ever-greater pay raises controlled all these industries and many more, with the full approval of the then-reigning Labor Party. But as the Conservative Party’s mercilessly witty campaign slogan put it, “Labor Isn’t Working.”

James Callaghan, the Labor prime minister, failed to see the trouble, telling a reporter in 1979, “I don’t think that other people in the world would share the view that there is mounting chaos.” The Sun’s next-day headline would become a widely quoted catchphrase: “Crisis? What Crisis?”

Thatcher, who was schooled in the free-market theory of F.A Hayek, replaced Callaghan, crushed the striking unions, beat inflation (then in double digits) by tightening the money supply and unleashed the wealth creation of the marketplace by privatizing a huge chunk of the state-run economy.

Before Thatcher, British Airways, Rolls-Royce, BP, the phone system, the railroads and the gas company were all being run by government bureaucracies.

Victorian smokestack industries like coal and shipbuilding were dead but didn’t know it yet; Thatcher launched a boom in high-tech industries such as finance, aerospace and pharmaceuticals. Government spending plunged from 48 percent of the economy to 39 percent when she left office.

Far from being “heartless,” as she was frequently accused of being, she enabled middle-class strivers to prosper. Real per-capita income rose by a third during her tenure, then continued to shoot upward as market efficiencies multiplied.

Her many forceful one-liners — “There is no alternative,” “Don’t go wobbly on me, George” — bespoke a Britain that could swagger again and be proud of the country’s smashing victory over Argentina in the dispute over Britain’s Falkland Islands. One poll suggested 84 percent approval of Thatcher’s move to recapture the islands.

If her actions infuriated the left, it was her combative personality that earned her special enmity. Being right was bad enough — did she have to rub their noses in it?

Socialists, she said, “always run out of other people’s money.” When, at a meeting of fellow alleged Tories, someone suggested a “middle path” on economics, she slammed a copy of Hayek’s free-market tract “The Constitution of Liberty” on the table and said, “This is what we believe!”

She said “Communism and the [fascist] National Front both seek the domination of the state over the individual. They both, I believe, crush the right of the individual. To me, therefore, they are parties of a similar kind . . . The National Front is a socialist front.”

Yet her agonized final chapter, a decade-long Alzheimer’s decline, sympathetically chronicled by Oscar-winner Meryl Streep in her surprisingly pro-Thatcher movie, “The Iron Lady,” seemed a cruel joke, a reminder that she could be defeated only from within, never without (as when her intransigence on a 1990 tax led to her ouster at the hands of her own party).

Today, her warnings about the effects of European economic union are beginning to sink in. The Iron Lady is a permanent figure standing watch over Britain.